High radio-frequency wattmeter



Aug. 31, 1948. J, QVREBQ 2,448,044

HIGH RADIO FREQUENCY WATTHETER Filed Dec. 23, 1944 2 Sheets-Sheet 1 Aug. 31, 194s. P. J. OVREBO 2,448,044

HIGH RADIO FREQUENCY WATTME'I'ER Filed Dec. 23, 1944 2 Sheets-Sheet 2 III III I l/ INVENTOR. pm Jfl/fiifl BY 49mm QM.

Patented Aug. 31, 1948 UNITED STATES PATENT OFFICE amp HIGH RADIO-FREQUENCY WATTMETEB rm 1. oval. who. Ohio Application December 28. 1044. Serial No. 569,571 17 Claims. (L 171-95) (Granted under the nine relates to high radio- The output of a radiofrequency transmitter or generator is fed through a coaxial line, of desired impedance, to a thermocouple and attenuating cable with appropriate terminating resistor which is shunted across a calibrated indicating instrument, whose function is to measure the D. C. current or D. C. E. M. F. set up by the thermocouple. This current or E. M. F. is a measure of the radio frequency power or radio frequency voltage of the radio frequency source.

An object of the invention is to measure the radio frequency power output of a transmitter or other radio frequency generator, or to measure the power made available at any place in a circuit. A further object of measure the radio frequency voltage of a transmitter or other radio frequency generator, or the potential difference available at any place in a circuit.

A further object of the invention is to provide a means, by a high-loss line and a terminating resistor, whereby radio frequency energy may be continuously or intermittently dissipated while the source of radio frequency energy is in operation or is being tested, modified or repaired.

It is a further object of this invention to provide a sensitive means of measuring the power output, or voltage output, or current output of a radio frequency transmitter or generator while the same is in operation, or is being tested, modifled or repaired.

These and other objects will appear through the specification and will be pointed out in the claims.

The measurement of radio-frequency output, in the form of power, voltage or current, is very desirable for control purposes. Since the output of radio frequency transmitters and generators involves energy, it is necessary that means be provided for the dissipation of this energy without injury to the prime source, or the measuring equipment. It is likewise important to prevent this energy from being radiated in the form of radio waves in sufficient amounts to cause interference or to betray the source as to location, frequency or other characteristic.

A novel feature of this device is that a coolin airblast is provided to aid in the dissipation of the invention is to m of March a, no. as nded April :0.

the heat produced by the attenuation of the radio frequency energy.

This new radio frequency wattmeter is easily adaptable to the measurement of power, voltage and current from radio frequency transmitters or other radiofrequency generators up to 1500 megacycles, with power outputs between 2 and 500 watts, whether such transmitters or generators be inductively or capacitatively coupled. It is further anticipated that by substitution of a more sensitive current meter and with the addition of coaxial cable to the attenuating line, which has low attenuation at the medium and normall high frequencies, and an effective amount of attenuation at the very high frequencies, both very low powers and very high frequencies may be added to the above range of effectiveness.

A further feature of the invention is that the wattmeter requires no matching section and measures power or the related quantities in terms of the deflection oi a 0-1, D. C. milliammeter or other sensitive meter. At very high frequencies, the radio frequency energy is completely attenuated by the high-loss coaxial cable, while at the medium high and low frequencies the attenuation is accomplished by both the high-loss cable and the terminating resistor. At the low and very low frequencies, the attenuation is accomplished almost entirely by the terminating resistor. With the addition of low loss cable, the attenuation of the ver high radio frequencies can be accomplished over a reasonable length of eagle instead of a very short length of high loss ca le.

Referring to the drawings wherein like numerals denote like parts,

Fig. 1 is a vertical elevation of the wattmeter with the cover housing cut away to show the lossline and blower arrangement. The loss-line is partially shown to reveal the core structure.

Fig. 2 is a right end elevation of the wattmeter shown in Fig. 1.

Fig. 3 is a sectional view of the wattmeter taken on the line 3-3 of Fig. 1.

Fig. 4 s an enlarged cross-sectional fragmentary view of the resistor and inner core shown in Fig. 1.

. Fig. 5 is a schematic diagram view of the blower and pilot lamp circuit.

Fig. 6 is a schematic diagram view of the wattmeter circuit employing inductive coupling to a transmitter. I i

Fig. 7 is a similar view to that of Fig. 6 employing capacitative coupling to the transmitter and using a shorting bar tuner so as to provide a drives a turbo-fan or blower for forcing air D. C. return circuit for the thermocouple current around the loss-line cable It! to dissipate the and at the same time provide a radio frequency heat generated therein by the passage of the open circuit so as not to disturb the circuit. The transmitter output current.

shorting bar tuner can be set for different fre- The blower 28 is shown in Fig. 1 as mounted quencies. Opposite the resistor H, which is enclosed in the inner core 24 and spaced therefrom by spacers 29.

Thermocouple ammete' The resistor I I. shown in cross-section in Fig.

The signal from the transmitter I0 is fed induc- 41 is preferably cemm'ic tube 39 having on its l0 outer surface a resistive carbon coating 3|. Plugs uvely to the coaxial fflgg ffg z tfi f fi 32 and 33 close the ends of the ceramic tube 30, rably removably connected and form contact with the carbon coating 3|. into the loss-line by screw couplings so that it is The central f 9 1055 11116 easily replaceable with other thermocouples of extends togethel'r 41h d ellectrgg coatilrig 5, the same or different sensitivity so as to provide 'thmugh the ho low bore of so at M? is insulated from plug 32 but forms electric-a1 the desired sensitivity range to measure power, voltage or current. The thermocouple is prefereon'taot wlt'h plug mmugh a taper-ended t'or bar 31, the electrical circuit being comably made a part of the central conductor of the nee coaxial cable. However, it ma under special cirmeted from cable sheath conduibor 36 P1118 cumstances be made a part of the outer conducm'teriorly tapered tel'mmaimlg plug to tor The thermocouple may be of any type but silver coating 39 and carbon coating 3|, silver is preferably to be of a eoaxially, impedance coating plug and and to Inner t whose thermocou 1e element com coaxial conductor 34 through taper bar 31. The gg 'fi i gzi lengths of Nlchmgle and constam carbon coating 3| thereby forms a considerable tin or equivalent, with silver soldered twisted resistive surface between mnel: and outer joints matched to the standard by means of clip ductors of the loss-line, and will emit considerping the lengths of the twist. The thermocouple able heat which is driven out of inner core Ii is connected into the high-loss line I3, preferby blower Connector bar 31 has its ends ably 100 feet in length for field use, and of longer tapered matchlthe l plugs lengths for more precise laboratory or test work. and to minimize stendmg waves This line is terminated in a 50 ohm resistor when The less is heueany wound about the impedance of the loss-line and connecting pair of coaxial eoresinner ewe being coaxial cable is 50 ohms. It is preferably to be sumclen'tly in diameter than the 011m of the same value as the impedance of the line, f or name 25 mm an speee will formed as chosen for the impedance of the transmitter 35 bmween the helices of coiled F M or generator. At high frequencies, most of the one end of the mner core 'there 15 provided preferably the terminating 'I'GSI'SUOI' l4, and at the other end the motor-driven turbo-fan 22 for creating a constant blast of cooling air through the 50 ohm resistor It 40 the inner core 24. A baiile 26 at the opposite I end of inner core 24, and spaced therefrom, g g gggii g gg g g i z gg g fi gi gf reverses the flow of cooling air and directs it eramuredifirenulal principle for metals of into and through the outer core, across both coils fer nit themmekcmc wer' increases with m of loss-line, and then out of the housing 21 which poser output of the trfgsmmten The houses the component parts of the complete w attli I f 1 s: g gg z z figi zg gzifii gm i fi 23:3: Since the various parts of the meter which are any a maxialdtype cab1e In ms circuit are com subject i resistive heating are contained within of the transmitter coupling ,tmn-sfomer l2 ten air blast and cooled to a temperature sufficiently low to avoid disintegration from excessive heatmina-tlng resistor H, a pair of choke coils l5 and IS, a capacitor i1 and a milliammeter, or micro- The cores and may be of m series with the owner, or capacitor is circumferen tially spaced rods 25, the object being is such that any residual radio frequency current advantageously exposed to blast of cool is prevented from reaching the meter l8, which There is thus Provided a compact arrangement then measures only the D. C. output current of employing a cooled loss-line which permits spacthe thermocouple H. The direct current sets up ing of the sensitive milltam meter at a distance a drop in potential across the terminating refrom the line and thermocouple heat so that it sistor M. This drop in potential or current is may be mounted anywhere on the housing 21. me sur d y the meter 8 which may be 081- The novel construction permits also the use ibrated in terms of radio-frequency Dowe 0 tof the same transmission line to transmit D. C. age cummi to the milliameter and to dissipate the radio Blower circuit frequency energy at all frequencies. This con- Tapped mm the power line feeding the trans struction eliminates the difliculty of filtering out mitter, but preferably separate from the lossmdio'frequency current where separate line circuit, is a blower and pilot light circuit. leads are 'prevlded fmm meter ee'eh the This circuit is broken by motor switch 2|. When themocouple elemen'ts- I11 addmon to these the circuit is closed, motor 22 and pilot lamp advambages the thermocouple elements may be 23 e energlzed The u it i s n t ct as removed and replaced in the lead line at will will be hereinafter described, that the motor without necessitating impedance-adjusting any partofthecircuitoroftuning the ilnetoreaonate at the different frequencies being tested.

While the invention has been illustrated and described in its preferred embodiment, it is contemplate-d that changes in the details, materials, form, and construction thereof may be made without departing from the spirit or scope of the invention as claimed.

What I claim is:

1. A radio-frequency wattmeter including an electrical loss-line conductor adapted for connection to a source of radio frequency energy. and ventedly mounted in a confined area, an electrical resistor interiorly proportioned and shaped at its opposite termini to minimize standing waves, a thermocouple, and a current measuring milliamineter and, in a separate circuit, a cooling blower, said blower being mounted so as to continuously force a blast of cooling air across the loss-line, thermocouple and resistor while measuring current.

2. A radio frequency wattmeter comprising means for dissipating the input current, thermocouple means for generating a measurable electromotive force, a coaxial element resistor having matched taper terminations to provide a low standing wave characteristic for dissipating the input current in addition to said first-mentioned dissipating means, means for measuring said electromotive force, and cooling means for dissipatlng the resistive heat of the input current.

3. A radio-frequency wattmeter comprising a predetermined length of loss-line coaxial electrical conductor helically wound over a hollow core, and adapted to be connected at its input end to a source of radio-frequency current: a resistor interiorly proportioned and shaped at its opposite termini to minimize standing waves at the output end of said line to further dissipate currents passed by said loss line, a milliammeter connected between the inner and outer conductors of said loss line, and a thermocouple connected into the inner conductor of said loss line and milliammeter for generating an electrometive force or current indirect ratio to the power input to said loss line.

4. A radio frequency wattmeter comprising a predetermined length of loss-line coaxial cable helicaily wound over a pair of spaced coaxial cores suitably baffled to provide, air ducts for forced draft to facilitate cooling, inductive coupling means for coupling said line to the output of a radio frequency transmitter, said line circuit including a loss line resistor for power dissipation in addition to the loss line dissipation, a thermocouple, a sensitive meter for measuring the thermocouple-generated direct current, inductance and capacitance means across which said sensitive meter is shuntedly connected, for filtering out radio frequency current from the direct current being measured, and cooling means directing a blast of air around said line,

5. A radio frequency wattmeter comprising housing means, supporting means contained in said housing means, high-loss line means wound on said supporting means, thermocouple means incorporated in said line means, means terminating said line means in its characteristic impedance, and blower means for cooling said line means and said terminatingmeans.

6. A radio frequency wattmeter comprising housing means, supporting means contained in said housing means, high-loss line means wound on said supporting means, thermocouple means incorporated in said line means, means terminating said line means in its characteristic impedance, metering means for measuring directcurrent flow in said terminating means, filtering means connected between said terminating means and said metering means, and blower means for cooling said line means and said terminating means.

'l. A 'radio frequency wattmeter comprising housing means, supporting means contained in said housing means, high-loss line means wound on said supporting means, thermocouple means incorporated in said line means, means terminating said line means in its characteristic im pedance, metering means for measuring the direct-current potential across said terminating means, filtering means connected between said terminating means and said metering means, and blowermeans for cooling said line means and said terminating means. i

8. A radio frequency wattmeter comprising a housing, a plurality of supports coaxially arranged in said housing, a-high-loss line wound on said supports forming coaxial layers, a thermocouple incorporated in said line and a resistor terminating said line in its characteristic impedance.

9. A radio frequency wattmeter as set forth in claim 8, wherein said line is helicaily wound on said supports.

10. A radio frequency wattmeter as set forth in claim 8, wherein said line forms a plurality of helices, said supports being the cores of said helices.

11. A radio frequency wattmeter comprising a housing, a plurality of core forming means contained in said housing, said cores being coaxially,

related, a high-loss coaxial line helically wound on said cores forming a plurality of coaxial helices, thermocouple means incorporated in said line, and a resistor terminating said line in its characteristic impedance. 12. A radio frequency wattmeter comprising a housing containing a first core forming means and at least a second core forming means, said second core having a diameter greaterthan said first core, said cores being coaxially related, a high-loss coaxial line helicaily wound on said coresand forming inner and outer serially connected coaxial helices, thermocouple means in corporated in the inner conductor of said line, and a resistor terminating said line in its char acteristic impedance, said resistor being disposed within said first core. 7

13. A radio frequency wattmeter comprising a housing containing a first core forming means and at least a second core forming means, said second core having a diameter greater than saidfirst core, said cores being coaxially related, a high-loss coaxial line helically wound on said cores and forming inner and outer serially con nected coaxial helices, said helices being spaced from each other and forming an air passage, thermocouple means incorporated in the inner conductor of said line, a resistor terminating said line in its characteristic impedance, said resistor being disposed within said first core, a battle spaced from one end of said first core, and blower means directed into the other end of said corswhereby cooling air forced through said first care, over said resistor, is reversed by said baille to flow through said passage.

14. In a radio frequency wattmeter comprising a high-loss coaxial line and a thermocouple in Z- sald linemeans terminatingsaid line comprising a ceramic cylinder, a resistive coating on the exsaid first plug, the other end of said bar being insulated from said second plug, and means insulated 'from said second plug for connecting the inner conductor oi said line to the latter end 01' said bar. the outer conductor of said linebeing connected to said second plug.

8'. of a coaxial line, and .wherein the niaanitndc oi said current is responsive to the radiotrequency power introduced in said line. the combination with said thermocouple, meter and line 01a plurality of core forming means, a plurality othelices PAUL J. I

REFERENCES CITED d The following references are. of record'in the- 15. In a resistor as set forth in claim 14, where-, 15 me of this patent;

in said resistive coating is oi carbon, a silver coatlng connecting said carbon coating and said plugs.

16. In a resistor said plugs are interiorly tapered, said or standing waves is minimized.

17. In a radio frequency wattmeter wherein a meter-measures the current generated by a ther-" mocouple incorporated in the inner conductor- :a

as set forth in claim 14,

UNITED STATES PATENTS 

